foreword
When I was brushing the questions, I saw that someone wrote the code and used {
{}}the wording method. I have never seen it before, so I hereby record it.
Queue<TreeNode> queue = new LinkedList<>() {
{
add(root); }};
a brief introdction
example
{
{}}This method is to initialize a collection, avoiding adding one by one to the collection initialization.
ArrayList<String> list = new ArrayList<String>(){
{
add("A");
add("B");
add("C");
}};
// 和下面功能实现一样
// ArrayList<String> list = new ArrayList<String>();
// list.add("a");
// list.add("b");
// list.add("c");
understand
first bracket
//定义了一个继承于ArrayList的类，它没有名字
new ArrayList<String>(){
//在这里对这个类进行具体定义
};
The brackets here represent a specific definition of a class.
second parenthesis
new ArrayList<String>(){
{
//这里是实例初始化块，可以直接调用父类的非私有方法或访问非私有成员
}
};
The brackets here indicate the instance initialization block (Instance Initialiazer Block), also known as the non-static initialization block.
Analogous to static initial block
static{
//静态初始块
}